BIOL 2252 – Chapter 22: The Immune System (Innate & Adaptive Defenses)

89 vocabulary flashcards summarizing key immune-system terms from BIOL 2252 Chapter 22, spanning innate defenses, adaptive responses, cells, molecules, and immunological principles.

Pathogen

Any infectious agent capable of causing disease in a host.

Bacteria

Prokaryotic, single-celled microbes; most harmless, some virulent (e.g., Clostridium tetani).

Virus

Non-cellular particle of DNA or RNA in a protein capsid; obligate intracellular parasite.

Fungus

Eukaryotic organism with cell wall; produces spores and proteolytic enzymes (e.g., yeast).

Protozoan

Eukaryotic, wall-less parasite that lives intra- or extracellularly (e.g., malaria parasite).

Multicellular Parasite

Macroscopic eukaryote that lives in host and steals nutrients (e.g., tapeworm).

Prion

Infectious protein fragment that damages nervous tissue (e.g., mad-cow disease).

Leukocyte

White blood cell formed in red bone marrow; key player in immunity.

Granulocyte

Leukocyte with cytoplasmic granules: neutrophil, eosinophil, basophil.

Neutrophil

Most abundant phagocytic granulocyte; first cellular responder to infection.

Eosinophil

Granulocyte that attacks parasitic worms and participates in allergy/asthma.

Basophil

Circulating granulocyte that releases histamine and heparin to promote inflammation.

Monocyte

Agranulocyte that becomes a macrophage upon leaving bloodstream.

Macrophage

Large phagocyte derived from monocyte; chief eater and antigen-presenter.

Lymphocyte

Agranulocyte comprising B cells, T cells, and natural killer (NK) cells.

B-Lymphocyte

Lymphocyte that matures in bone marrow and mediates humoral immunity by producing antibodies.

T-Lymphocyte

Lymphocyte that matures in thymus; mediates cellular immunity.

Natural Killer (NK) Cell

Large granular lymphocyte that induces apoptosis in abnormal cells using perforin and granzymes.

Primary Lymphoid Organ

Site of lymphocyte formation and maturation: red bone marrow & thymus.

Secondary Lymphoid Structure

Site where lymphocytes are activated: lymph nodes, spleen, tonsils, MALT, etc.

Mast Cell

Connective-tissue cell that releases histamine, heparin, and eicosanoids to intensify inflammation.

Cytokine

Small protein messenger released by immune cells to regulate immunity (e.g., interleukins, interferons).

Innate Immunity

Nonspecific defenses present at birth; include barriers, cells, chemicals, inflammation, fever.

Adaptive Immunity

Specific, acquired immunity involving T and B lymphocytes; exhibits memory and specificity.

First Line of Defense

External surface barriers: intact skin and mucous membranes with antimicrobial secretions.

Second Line of Defense

Internal innate mechanisms: phagocytes, NK cells, interferon, complement, inflammation, fever.

Third Line of Defense

Adaptive immune response mediated by T and B lymphocytes.

Phagocyte

Any cell that engulfs and digests pathogens—mainly neutrophils, macrophages, dendritic cells.

Dendritic Cell

Professional antigen-presenting cell that links innate and adaptive immunity.

Respiratory Burst

Rapid release of reactive oxygen species by phagocytes to kill resistant microbes.

Opsonization

Coating of pathogen with opsonin (antibody/complement) to enhance phagocytosis.

Histamine

Inflammatory chemical causing vasodilation and increased capillary permeability.

Heparin

Anticoagulant released by basophils and mast cells during inflammation.

Eicosanoid

Lipid mediator (e.g., prostaglandin, leukotriene) that intensifies inflammation.

Apoptosis

Programmed cell death without lysis, often induced by cytotoxic T or NK cells.

Perforin

Pore-forming protein released by NK and cytotoxic T cells.

Granzyme

Serine protease entering target cells through perforin pores to trigger apoptosis.

Interferon (IFN)

Antiviral cytokine that inhibits viral replication and activates NK cells and macrophages.

Complement System

30 plasma proteins that enhance immunity via opsonization, inflammation, and cytolysis.

Classical Pathway

Complement activation route initiated by antibody-antigen complex.

Alternative Pathway

Complement activation by direct binding to microbial polysaccharides.

Membrane Attack Complex (MAC)

Complement-formed pore causing cytolysis of target cell.

Inflammation

Localized, nonspecific response to injury or infection characterized by redness, heat, swelling, pain.

Chemotaxis

Movement of leukocytes toward chemical attractants at injury site.

Margination

Leukocyte adhesion to endothelial CAMs inside blood vessels during inflammation.

Diapedesis

Passage of leukocytes through capillary walls into tissues.

Exudate

Protein-rich fluid that leaks into tissues during inflammation.

Kinin

Plasma protein (e.g., bradykinin) that promotes pain, vasodilation, and permeability.

Fever

Systemic rise in body temperature induced by pyrogens to hinder microbes and boost immunity.

Pyrogen

Substance (e.g., IL-1) that resets hypothalamic thermostat to produce fever.

Antigen

Substance that evokes an adaptive immune response by binding BCR or TCR.

Immunogen

Antigen capable of triggering an immune response.

Epitope (Antigenic Determinant)

Specific region of antigen recognized by immune receptor or antibody.

Hapten

Small molecule that becomes immunogenic only when attached to a carrier.

MHC (Major Histocompatibility Complex)

Cell surface glycoproteins that present peptide antigens to T cells.

MHC Class I

Self-protein on all nucleated cells; presents endogenous peptides to CD8 cytotoxic T cells.

MHC Class II

Protein on professional APCs; presents exogenous peptides to CD4 helper T cells.

Antigen-Presenting Cell (APC)

Cell (dendritic, macrophage, B cell) that processes and displays antigen with MHC to T cells.

Positive Selection

Thymic test ensuring T cells can bind self-MHC molecules.

Negative Selection

Thymic elimination of T cells that strongly bind self-antigens (self-tolerance).

Clonal Selection

Proliferation of lymphocyte clone after binding its specific antigen.

Helper T Cell (Th, CD4+)

T cell that coordinates immune responses via cytokine secretion.

Cytotoxic T Cell (Tc, CD8+)

T cell that kills infected or abnormal cells using perforin and granzymes.

Regulatory T Cell (Treg)

CD4+ cell that suppresses immune responses to maintain tolerance.

Memory Cell

Long-lived B or T lymphocyte formed after activation, enabling faster secondary response.

Plasma Cell

Activated B cell that secretes large quantities of antibodies.

Humoral Immunity

Antibody-mediated defense against extracellular pathogens.

Cell-Mediated Immunity

T-cell-driven defense against intracellular pathogens and abnormal cells.

Antibody (Immunoglobulin)

Y-shaped protein produced by plasma cells that binds specific antigens.

IgG

Most abundant serum antibody; crosses placenta; dominant in secondary response.

IgM

Pentameric antibody first released during primary response; potent agglutinator.

IgA

Dimeric antibody in secretions (saliva, milk, mucus) that guards mucosal surfaces.

IgD

Monomer serving mainly as B-cell receptor.

IgE

Antibody bound to basophils/mast cells; mediates allergies and parasitic defense.

Neutralization

Antibody blocks pathogen’s binding sites, rendering it harmless.

Agglutination

Antibody cross-links cells, forming clumps for easier clearance.

Precipitation

Antibody cross-links soluble antigens into insoluble complexes.

Complement Fixation

Antibody initiates complement cascade leading to cell lysis.

ADCC (Antibody-Dependent Cell-Mediated Cytotoxicity)

NK cell killing triggered by Fc binding of antibodies on target cell.

Primary Immune Response

Slow initial adaptive reaction after first antigen exposure; generates memory cells.

Secondary Immune Response

Rapid, robust reaction upon re-exposure due to memory lymphocytes.

Active Immunity

Long-term protection produced by direct antigen exposure and antibody formation.

Passive Immunity

Short-term protection via transfer of ready-made antibodies (e.g., maternal IgG).

Herd Immunity

Population-level resistance achieved when a high percentage is immune, limiting pathogen spread.